Pressure compensation valve unit and pressure oil supply system utilizing same

ABSTRACT

A pressure compensation valve unit comprises a check valve which is pushed in an opening direction thereof by an inlet side pressure and in a closing direction thereof by an outlet side pressure and a pressure reducing valve actuating to establish communication between the inlet side and the outlet side and block the communication therebetween, pushed in the blocking up direction by a pressure in a pressure receiving chamber to push the check valve in the closing direction thereof, pushed in the communication direction with a highest pressure in a plurality of pressures by a pressure selective receiving means, and communicating the outlet side with the pressure chamber, and a pressure oil supply system is provided with the pressure compensation valve unit of the structure described above.

TECHNICAL FIELD

The present invention relates to a pressure compensation valve unit of apressure oil supply system for supplying a discharge pressure oil fromone hydraulic pump to a plurality of actuators and a pressure oil supplysystem utilizing the pressure compensation valve unit.

BACKGROUND ART

As a pressure oil supply system for supplying discharge pressure oilfrom one hydraulic pump to a plurality of actuators, there is known asystem shown in, for example, Japanese Patent Laid-open Publication No.HEI 4-244604.

In such system, as shown in FIG. 1, a plurality of pressure compensationvalve units 3 are connected in parallel to a discharge passage 2 of onehydraulic pump 1, and a plurality of actuators 5 are connectedrespectively to outlet sides of the respective pressure compensationvalve units through a plurality of directional control valves 4 in amanner such that when the plurality of actuators 5 are simultaneouslyactuated, the respective pressure compensation valve units 3 are set inaccordance with the highest load pressure to thereby to be able tosupply the discharge pressure oil from one hydraulic pump 1 to theactuators 5 which are of different loads, respectively.

Each of the pressure compensation valve units 3 is provided with a checkvalve 6 and a pressure reducing valve 7. The check valve 6 is pushed ina valve opening direction by a inlet pressure introduced into a pressurechamber a and in a valve closing direction by an outlet pressureintroduced into pressure chamber b, and the outlet side of the checkvalve 6 is communicated with a pump port 4a of the directional controlvalve 4. The pressure reducing valve 7 is pushed in a valve openingdirection by a load pressure of a corresponding actuator 5 introducedinto a pressure chamber c via a load pressure introducing passage 8 andis pushed in a valve closing direction by a spring force of a spring 9having a weak spring force and an outlet pressure introduced into apressure chamber d. The pressure reducing valve 7 is provided with apush rod 10 for pushing the check valve 6 in its closing direction, sothat the communication between the inlet side and the outlet sidethereof is established and blocked and the check valve 6 is pushed inits closing direction by the pressure difference between a load pressureof an actuator 5 acting on a pressure receiving portion c and a pressureacting on a pressure receiving portion d the communication between theinlet side and the outlet side thereof is established and blocked.

The outlet sides of the respective pressure reducing valves 7 arecommunicated with load pressure detection passages 11, respectively,which are communicated with a tank 13 through a throttle passage 12.

The hydraulic pump 1 has a variable capacity structure, and an angle ofa swash plate 14 of the hydraulic pump 1 is changed by an adjustingcylinder 15 to which pump discharge pressure is supplied by thedirectional control valve 16 for a pump operation adjustment. Thedirectional control valve 16 for pump operation adjustment is pushed tothe discharge side by the spring force of a spring 17 and a loadpressure in the load pressure detection passage 11 and is pushed to thecommunication side by the pump discharge pressure.

As mentioned above, when a plurality of actuators 5 are operated all atonce, the pressure reducing valve 7 of the pressure compensation valveunit 3 connected to one actuator 5 having a large load (for example, anactuator 5, lefthand one as viewed in FIG. 1) is pushed rightward toestablish communication between the inlet and outlet sides thereof,whereby the large load pressure acts on the pressure receiving portion dof the pressure reducing valve 7 of the pressure compensation valve unit3 connected to another one actuator 5 having a small load (for example,an actuator 5, righthand one, as viewed in FIG. 1). At this time, sincethe load pressure acting on the pressure receiving portion c of thepressure reduction valve 7 is small, this pressure reduction valve 7 ispushed leftward to block the communication between the inlet and outletsides thereof and the check valve 6 is also pushed in a valve closingdirection to reduce the opening area thereof. Accordingly, a highpressure oil for compensating for the large load is supplied to thelefthand actuator 5 and a low pressure oil for compensating for thesmall load is supplied to the righthand actuator 5.

There is known a pressure compensation valve having a concrete structureof the above-mentioned pressure compensation valve unit 3, for example,as disclosed in Japanese Utility Model Laid-open Publication No. HEI5-42703.

The concrete structure thereof is shown in FIG. 2, in which a spool bore34, a check valve bore 35 and a pressure reducing valve bore 36 areformed to a valve body 20 of the directional control valve 4. A mainspool 37 is inserted into the spool bore 34 for communicating the spoolbore with an inlet port, a load pressure detection port, an actuatorport, a tank port, etc. all opened thereto or for blocking thecommunication therebetween, thus constituting the directional controlvalve 4. Further, a spool 23 is inserted into the check valve bore 35for communicating this bore with an inlet port 21 and an outlet port 22opened thereto or for blocking the communication therebetween, thusconstituting the check valve 6. Furthermore, a spool 26 is inserted intothe pressure reducing valve bore 36 for communicating this bore with afirst port 24 and a second port 25 opened thereto or for blocking thecommunication therebetween, a first pressure receiving chamber 27 and asecond pressure receiving chamber 28 are formed on respective end sidesof the bore 36, and the spool 26 is pushed leftward as viewed in FIG. 2to abut against the spool 23 of the check valve 6, thus constituting thepressure reducing valve 7.

Further, it is to be noted that since only the load pressure of thecorresponding actuator (called hereafter corresponding load pressure)acts on the pressure receiving portion c of the pressure reducing valve7 of the pressure compensation valve unit 3 mentioned above, it isalways necessary to locate one pressure compensation valve unit 3 to oneactuator 5.

For example, with reference to FIG. 1, in a case where the output sideof the lefthand pressure compensation valve unit 3 is connected, withoutdisposing the righthand pressure compensation valve unit, to the pumpport 4a of the righthand directional control valve 4 through a circuit18, the load pressure of the righthand actuator 5 is not related at allto the pressure compensation and such load pressure is not applied tothe load pressure detection circuit 11, so that, when the load pressureof the lefthand actuator 5 is high at the time of simultaneouslyoperating two actuators shown in FIG. 1, the high load pressure isapplied to the pressure receiving portion c of the pressure reducingvalve 7 and, hence, the pressure compensation valve unit 3 tends tooutput a high pressure corresponding to the high load pressure. However,since the output side of the check valve 6 is connected to the righthandactuator 5 of low load pressure, much oil flows.

On the other hand, when the load pressure of the righthand actuator 5 ishigh, the high load pressure does not act on the pressure receivingportion c, on which low lefthand pressure load acts, and hence, thepressure compensation valve unit outputs a pressure corresponding to thelow load pressure to thereby operate only the lefthand actuator 5 (whenthe lefthand actuator reaches its stroke end, the righthand actuator isoperated). In the load pressure detection circuit 11, the low loadpressure is detected and the hydraulic pump provides a capacitycorresponding to this low load pressure.

The above matters will be applicable to a case where pressure oil issupplied to three or more actuators.

In the foregoing explanation, the reason why the capacity of thehydraulic pump is made to a value corresponding to the load pressure isto reduce the capacity of the hydraulic pump 1 at the neutral positionof the directional control valve 4 so as to reduce drive horse powerloss of the hydraulic pump because the directional control valve is of aclosed center type structure capable of blocking up the pump port 4a atthe neutral position of the directional control valve 4. It is notnecessary to locate the load pressure detection circuit 11 in a casewhere the above matter is ignored, an unload valve is disposed, or adirectional control valve of an open center type structure is utilizedin which the pump port 4a is communicated with the tank in an operationat the neutral position of the directional control valve.

The present invention was conceived to improve the above-mentioneddefects and to provide a pressure compensation valve unit and a pressureoil supply system capable of supplying pressure oil to a plurality ofactuators regardless of the magnitude of the load pressure, whereby thenumber of the compensation valves can be reduced less than the number ofthe actuators, thus reducing manufacturing cost.

DISCLOSURE OF THE INVENTION

To achieve the objects described above, according to the firstembodiment of the present invention, there is provided a pressurecompensation valve unit comprising a check valve which is pushed in anopening direction thereof by an inlet side pressure and in a closingdirection thereof by an outlet side pressure and a pressure reducingvalve actuating to establish communication between the inlet side andthe outlet side and block the communication therebetween, pushed in theblocking up direction by a pressure in a pressure receiving chamber topush the check valve in the closing direction thereof, pushed in thecommunication direction with a highest pressure in a plurality ofpressures by a pressure selective receiving means, and communicating theoutlet side with the pressure chamber.

According to the above structure, since the pressure reducing valve ofthe pressure compensation valve unit is pushed in the directioncommunicating the inlet and outlet sides by the highest load pressure inthe plurality of load pressures, the pressure compensation of the supplypressure oil can be performed by the highest load pressure in theplurality of load pressures.

Therefore, the pressure oil can be supplied to the plurality ofactuators regardless of the magnitude of the load pressure even if thepressure oil is supplied to the plurality of actuators through onepressure compensation valve unit, so that the number of the pressurecompensation valve unit is reduced less than that of the actuators,reducing the cost.

In the above structure, it is desired that the pressure selectivereceiving means is provided with a slider for pushing the pressurereducing valve in the communication direction thereof and a pressurereceiving portion adapted to receive a pressure for pushing the pressurereducing valve in the communication direction and wherein when apressure acting on the slider is higher than a pressure acting on thepressure receiving portion, the pressure reducing valve is pushed by theslider in the communication direction thereof.

Otherwise, it is desired that the pressure selective receiving meanscomprises a pressure receiving portion receiving a pressure for pushingthe pressure reducing valve in the communication direction and a highpressure priority valve for supplying a pressure oil on the highestpressure side in a plurality of pressure oils to the pressure receivingportion.

According to the second embodiment of the present invention, there isprovided a pressure compensation valve unit which comprises:

a check valve provided with a check valve bore to which an inlet portand an outlet port are opened and a spool inserted into the check valvebore, adapted to communicate the inlet port with the outlet port and toblock the communication therebetween, pushed in the communicationdirection by a pressure at the inlet port and pushed in the blocking updirection by a pressure at the outlet port; and

a pressure reducing valve provided with a pressure reducing valve boreto which a first port and a second port are opened, a spool insertedinto the pressure reducing valve port, adapted to communicate the firstport with the second port and to block the communication therebetweenand having a small diameter rod opposing to the check valve, a thirdpressure receiving chamber receiving a pressure for pushing the spool inthe blocking up direction through the communication with the secondport, and first and second pressure receiving chambers formed on bothend sides of a free piston slidably fitted to the small diameter rod andadapted to receive a pressure for pushing the spool in the communicationdirection thereof,

wherein load pressures of different actuators are introduced into thefirst and second pressure receiving chambers.

In addition to this structure, it may be desired that a plurality offree pistons are fitted to the small diameter rod of the spool of thepressure reducing valve, a further pressure receiving chamber forreceiving a pressure for pushing the spool in the communicationdirection is formed between the adjacent free pistons, and loadpressures of other actuators to the other pressure receiving chambersare introduced.

According to the third embodiment of the present invention, there isprovided a pressure oil supply system wherein a pressure compensationvalve unit is disposed in a discharge passage of a hydraulic pump, thepressure compensation valve unit comprising:

a check valve which is pushed in an opening direction thereof by aninlet side pressure and in a closing direction thereof by an outlet sidepressure and a pressure reducing valve actuating to establishcommunication between the inlet side and the outlet side and block thecommunication therebetween, pushed in the blocking up direction by apressure in a pressure receiving chamber to push the check valve in theclosing direction thereof, pushed in the communication direction with ahighest pressure in a plurality of pressures by a pressure selectivereceiving means, and communicating the outlet side with the pressurechamber;

a plurality of actuators are connected to the output side of thepressure compensation valve unit through a plurality of directionalcontrol valves;

the discharge passage of said hydraulic pump is connected to the inletside of the pressure reducing valve of the pressure compensation valveunit; and

load pressure of the respective actuators are introduced into thepressure selective receiving means so as to push the pressure reducingvalve by the highest load pressure.

In this structure, it is also desired that the pressure selectivereceiving means is provided with a slider for pushing the pressurereducing valve in the communication direction and a pressure receivingportion receiving a pressure for pushing the pressure reducing valve inthe communication direction and wherein when a pressure acting on theslider is higher than a pressure acting on the pressure receivingportion, the pressure reducing valve is pushed in the communicationdirection by the slider.

Otherwise, it is desired that the selection pressure receiving meanscomprises a pressure receiving portion receiving a pressure for pushingthe pressure reducing valve in the communication direction and a highpressure priority valve for supplying a pressure oil on the highestpressure side in a plurality of pressure oils to the pressure receivingportion.

According to the fourth embodiment of the present invention, there isprovided a pressure oil supply system provided with a pressurecompensation valve unit comprising:

a check valve provided with a check valve bore to which an inlet portand an outlet port are opened and a spool inserted into the check valvebore, adapted to communicate the inlet port with the outlet port and toblock the communication therebetween, pushed in the communicationdirection by a pressure at the inlet port and pushed in the blocking updirection by a pressure at the outlet port; and

a pressure reducing valve provided with a valve bore for the pressurereducing valve to which a first port and a second port are opened, aspool inserted into the pressure reducing valve port, adapted tocommunicate the first port with the second port and to block thecommunication therebetween and having a small diameter rod opposing tothe check valve, a third pressure receiving chamber receiving a pressurefor pushing the spool in the blocking up direction through thecommunication with the second port, and first and second pressurereceiving chambers formed on both end sides of a free piston slidablyfitted to the small diameter rod and adapted to receive a pressure forpushing the spool in the communication direction thereof; and

wherein a plurality of actuators are connected to the output side of thepressure compensation valve unit through a plurality of directionalcontrol valves;

the discharge passage of the hydraulic pump is connected to the inletside of the pressure reducing valve of the pressure compensation valveunit; and

load pressure of different actuators are introduced into the first andsecond pressure receiving chambers of the pressure reducing valve tothereby push the pressure reducing valve in the communication directionwith the highest load pressure.

In this structure, it is also desired that a plurality of free pistonsare fitted to the small diameter rod of the spool of the pressurereducing valve, a further pressure receiving chamber for receiving apressure for pushing the spool in the communication direction is formedbetween the adjacent free pistons, and load pressures of other actuatorsto the other pressure receiving chambers are introduced.

In the above third and fourth embodiment, it is also desired that a loadpressure detection line is connected to the outlet side of the pressurereducing valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more clearly by the detailedexplanation described hereinafter and with reference to the accompanyingdrawings representing embodiments of the present invention. Further, theembodiments shown in the drawings are not made to specify the inventionand made for easy understanding of the invention.

In the accompanying drawings:

FIG. 1 is a hydraulic circuit diagram utilizing a conventional pressurecompensation valve unit.

FIG. 2 is a sectional view showing a concrete structure of the aboveconventional pressure compensation valve unit.

FIG. 3 is a hydraulic circuit diagram of a pressure oil supply systemequipped with a compensation valve unit according to a first embodimentof the present invention.

FIG. 4 is a sectional view showing a concrete structure of a directionalcontrol valve on one side in which the pressure compensation valve unitshown in FIG. 3 is assembled.

FIG. 5 is a sectional view showing a concrete structure of thedirectional control valve on the other side thereof.

FIG. 6 is a sectional view showing a concrete structure of the pressuresupply system shown in FIG. 3.

FIG. 7 is a sectional view showing another example of a directionalcontrol valve on the other side thereof.

FIG. 8 is a hydraulic circuit diagram of a pressure oil supply systemequipped with a compensation valve unit according to a second embodimentof the present invention.

FIG. 9 is a hydraulic circuit diagram of a pressure oil supply systemequipped with a compensation valve unit according to a third embodimentof the present invention.

FIG. 10 is a sectional view showing a concrete structure of adirectional control valve on one side in which the pressure compensationvalve unit shown in FIG. 9 is assembled.

FIG. 11 is a sectional view showing a concrete structure of the pressuresupply system shown in FIG. 9.

FIG. 12 is a hydraulic circuit diagram of a pressure oil supply systemequipped with a compensation valve unit according to a fourth embodimentof the present invention.

FIG. 13 is a hydraulic circuit diagram of a pressure oil supply systemequipped with a compensation valve unit according to a fifth embodimentof the present invention.

BEST MODE FOR EMBODYING THE INVENTION

Hereunder, the pressure compensation valve unit and a pressure oilsupply system provided with the pressure compensation valve unitaccording to preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

A first embodiment of the pressure oil supply system according to thepresent invention will be described with reference to FIG. 3, in whichlike reference numerals are added to members corresponding toconventional ones shown in FIG. 1 and detailed explanation thereof isomitted herein.

As shown in FIG. 3, on the side of the pressure receiving portion c ofthe pressure reducing valve 7 of the compensation valve unit 3, isdisposed a pressure selective receiving means 30 for pressing thepressure reducing valve 7 in a direction for communicating an inlet sideand an outlet side thereof with the highest load pressure in loadpressures of a plurality of actuators 5.

The pressure selective receiving means 30 is provided with a slider 31disposed between the check valve 6 and the pressure reducing valve 7,and the slider 31 is slidable in a direction toward the pressurereducing valve 7 by the pressure on a first pressure receiving portion32 and also slidable in a direction apart from the pressure reducingvalve 7 by the pressure on a second pressure receiving portion 33. Thefirst pressure receiving portion 32 is connected to a load pressuredetection port 4a of one of the directional control valve 4 through aload pressure introducing passage 8, and the second pressure receivingportion 33 is communicated with the pressure receiving portion c of thepressure reducing valve 7 and connected to a load pressure detectionport 4b of another one of the directional control valve 4 throughanother load pressure introducing passage 8.

Hereunder, the function of this embodiment will be described.

A load pressure PL of a lefthand actuator 5 in FIG. 3 acts on the firstpressure receiving portion 32 of the slider 31 and a load pressure PR ofa righthand actuator 5 acts on the second pressure receiving portion 33of the slider 31 and the pressure receiving portion c of the pressurereducing valve 7.

Under the state, when the lefthand load pressure PL is higher than therighthand load pressure PR, the slider 31 is slid on the side of thepressure reducing valve 7 to press the pressure reducing valve 7 in adirection for communicating the inlet side with the outlet side thereof.On the other hand, when the righthand load pressure PR is higher thanthe lefthand load pressure PL, the slider 31 is slid in a directionapart from the pressure reducing valve 7 and, at the same time, thepressure reducing valve 7 is pressed by the righthand pressure PR actingon the pressure receiving portion c in a direction for communicating theinlet side with the outlet side thereof.

Accordingly, the pressure on the outlet side of the pressurecompensation valve unit 3 is always compensated in pressure by thehigher pressure of the lefthand load pressure PL or the righthand loadpressure PR, and the outlet side pressure, i.e. load pressure, of thepressure reducing valve 7 corresponding to that higher pressure isdetected by the load pressure detection passage 11, in response to whicha capacity of the hydraulic pump 1 can be adjusted. Accordingly, in thetime when both the lefthand and righthand actuators 5 are simultaneouslyactuated, the pressure of a pressure oil supplied can be compensated bythe either higher one of the load pressures of the lefthand actuator 5and the righthand actuator 5, thus supplying the pressure oil, and insuch case, much amount of pressure oil is supplied to the actuator 5 onwhich a smaller load pressure is applied and the capacity of thehydraulic pump 1 corresponds to the higher load pressure, so that thepump discharge pressure increases in a short time to a pressurecorresponding to the higher load pressure.

FIG. 4 shows a concrete structure of the pressure compensation valveunit 3 used for the pressure oil supply system, and the pressurecompensation valve unit 3 is assembled in a valve block 40 of thedirectional control valve 4.

As shown in FIG. 4, the valve block 40 provides substantially arectangular parallelopiped shape. A spool bore 41 is formed to an upperside portion of the valve block 40 and is opened at its left and rightside surfaces 42 and 43 thereof, and on a lower side portion of thevalve block 40, are concentrically formed a check valve bore 44 openedto the left side surface 42 and a pressure reducing valve bore 45 openedto the right side surface 43. The valve block 40 is formed with a pumpport 46 opened to the spool bore 41, first and second load pressuredetection ports 47 and 48, first and second actuator ports 49 and 50 andfirst and second tank ports 51 and 52. Into the spool port 41, isinserted a main spool 53 having first and second small diameter portions54 and 55 and an intermediate small diameter portion 56. Further, thefirst and second load pressure detection ports 47 and 48 arecommunicated with each other.

The spool 53 is maintained at a neutral position A blocking up therespective ports by means of spring 57. When the spool 53 is slid in arightward direction, the spool 53 takes a first pressure oil supplyposition B via which the second actuator port 50 is communicated withthe second tank port 52 at the second small diameter portion 55, thepump port 46 is communicated with the second load pressure detectionport 48 via the intermediate small diameter portion 56, and the firstactuator port 49 is communicated with the first load pressure detectionport 47 at the first small diameter portion 54. When the spool is slidin a leftward direction, the spool 53 takes a first pressure oil supplyposition C at which the first actuator port 49 is communicated with thefirst tank port 51 via the first small diameter portion 54, the pumpport 46 is communicated with the first load pressure detection port 47via the intermediate small diameter portion 56, and the second actuatorport 50 is communicated with the second load pressure detection port 48via the second small diameter portion 55. These structures constitutesthe closed-center type directional control valve 4.

Into the bore 44 for the check valve 44, is inserted a spool 62 forestablishing and blocking the communication between an inlet port 60 andan outlet port 61 both opened thereto. The spool 62 takes a blocking upposition by means of a plug 63 so as not to be slid leftward from theillustrated position and is pushed to a communication position by aninlet pressure in the pressure receiving chamber 64, thus constitutingthe check valve 6. The outlet port 61 communicates with the pump port 46and the discharge passage 2 of the hydraulic pump 1 is connected to theinlet port 60, and the outlet port 61 is opened to a mated face of thevalve block 40 through a second communication hole 75.

A spool 66 provided with a rod 65 having a small diameter is insertedinto the pressure reducing valve bore 45, and the small diameter rod 65is opposed to the spool 62 of the check valve 6. Furthermore, a freepiston 67 as a slider 31 shown in FIG. 3 is inserted into the smalldiameter rod 65, and first, second and third pressure receiving chambers68, 69 and 70 are formed on both end sides and outer peripheral side ofthe free piston 67. The first pressure receiving chamber 68 correspondsto the first pressure receiving chamber 32 shown in FIG. 3, the secondpressure receiving chamber 69 corresponds to the second pressurereceiving chamber 33 and the pressure receiving portion c, and the thirdpressure receiving chamber 70 corresponds to the pressure receivingportion d shown in FIG. 3.

To the pressure reducing valve bore 45 are opened a first port 71 as aninlet port and a second port 72 as an outlet port, and the spool 66 isurged by a spring 73 having a weak spring force in a direction to blockup the first and second ports 71 and 72. The discharge passage 2 of thehydraulic pump 1 is connected to the first port 72 and the load pressuredetection passage 11 is connected to the second port 72. The firstpressure receiving chamber 68 is opened to the mated face of the valveblock 40 through the first communication hole 74 and the second pressurereceiving chamber 69 is communicated with the second load pressuredetection port 48 of the directional control valve 4 through an oil hole75.

Referring to FIG. 4, the spool 66 of the pressure reducing valve 7 isprovided with a central bore 66a into which the piston 67 is inserted tothereby constitute a pressure receiving chamber 77, which is opened tothe first port 71 through a fine hole 79, so that the pump dischargepressure oil fills the pressure receiving chamber 77, and since thepressure oil in the pressure receiving chamber 77 is flowed out througha throttle 79 when the spool 66 is slid in the communication direction(leftward as viewed), the sliding speed of the spool 66 in thecommunication direction is made slow.

This is a structure for slowly operating the pressure reducing valve 7at the time of variation of the load pressure and for making gentle thepressure variation of the pump discharge pressure, and hence, thisstructure may be eliminated.

As mentioned above, when the high pressure oil is flowed in the firstpressure receiving chamber 68, the free piston 67 is slid rightwardlyand presses the spool 66 in a direction for establishing thecommunication between the first and second ports 71 and 72. On the otherhand, when the highly pressurized oil is flown in the second pressurereceiving chamber 69, the free piston 67 is slid leftwardly to thestroke end position and presses the spool 66 in a direction forestablishing the communication between the first and second ports 71 and72, thus performing the same function as that of the pressurecompensation valve unit shown in FIG. 3.

The righthand directional control valve 4 concretely shown in FIG. 3 hasa structure represented by FIG. 5. That is, the structure of therighthand directional control valve 4 is the same as that of thelefthand directional control valve 4. However, the valve block 40 of thedirectional control valve 4 is not provided with the pressurecompensation valve unit 3, and the pump port 46 and the second loadpressure detection port 48 are opened to the mated face of the valveblock 40 through a third communication hole 76 and a fourthcommunication hole 77, respectively. Further, as shown in FIG. 6, whenthe valve blocks 40 of the righthand and lefthand directional controlvalves 4 are connected through the mated faces of both the valve blocks,the first communication hole 74 and the fourth communication hole 77 arecommunicated with each other, so that the pressure at the second loadpressure detection port 48 of the righthand directional control valve 4,i.e. the righthand load pressure, flows in the first pressure receivingchamber 68, and the second communication hole 75 and the thirdcommunication hole 76 are then communicated with each other, so that theoutlet side of the pressure compensation valve unit 3 is communicatedwith the pump port 46 of the righthand directional control valve 4 andthe output pressure (compensation pressure) of the pressure compensationvalve unit 3 also flows in the pump port 46 of the righthand directionalcontrol valve 4.

According to the structure described above, the valve blocks 40 areconnected to each other without arranging the load pressure introducingpassage 8 and the circuit line 8 shown in FIG. 3 as external linearrangement, thus making simple the line structure arrangement.

Furthermore, as shown in FIG. 5, since the valve block 40 of one of thedirectional control valves 4 has an extra space for incorporating thepressure compensation valve unit 3, this space can be utilized forlocating other elements such as other valve means.

For example, as shown in FIG. 7, the valve block 40 is formed with anauxiliary actuator port 80, and an auxiliary spool bore 81 is alsoformed through the auxiliary actuator port 80, the second load pressuredetection port 48 and the pump port 46. An auxiliary spool 82 isinserted into the auxiliary spool bore 81, and the auxiliary spool 82 isheld in an intermediate position blocking up these three ports by meansof a spring 83 and is slid to take a position for communicating thesethree ports by supplying a pressure oil of a hydraulic pump 85 into apilot pressure receiving chamber 84 through a pilot valve 86.Furthermore, the auxiliary actuator port 80 is communicated with an oilhole 88 of a block 87 connected to the valve block 40, and a reliefvalve 89 is provided for the block 87.

According to the structure described above, the output pressure of thepressure compensation valve unit 3 can be supplied to the oil hole 88 bysliding the auxiliary spool 82 between the neutral position and thecommunication position thereof through the actuation of the pilot valve86, and for example, the directional control valve 4 can be constructedas a control valve including no return circuit such as hydraulicallyoperational breaker.

Further, in a modification, a relief valve may be provided for the valveblock 40. An inlet opening opened on the inlet side of the relief valvemay be formed to the mated face of the valve block 40 so that the inletopening is communicated with the inlet opening 60 of the valve block 40provided for the pressure compensation valve unit 3 and the dischargeside of the relief valve is communicated with the first tank port 51 orthe second tank port 52.

According to this modified arrangement, the relief valve of thehydraulic pump 1 will be incorporated in the valve block 40 of thedirectional control valve 4.

In a further modification, an unload valve may be provided for the valveblock 40. A first inlet opening opened on the inlet side of the unloadvalve and a second inlet opening opened on the side of the pressurereceiving portion are formed to the mated surface of the valve block 40,respectively, so that the first inlet opening is communicated with theinlet opening 60 of the valve block 40 provided for the pressurecompensation valve unit 3 and the second inlet opening is communicatedwith the second port 72 and so that the discharge side of the unloadvalve is communicated with the first tank port 51 or the second tankport 52.

According to this modified arrangement, the unload valve of thehydraulic pump 1 will be incorporated in the valve block 40 of thedirectional control valve 4.

FIG. 8 represents the second embodiment of the pressure oil supplysystem according to the present invention. In this embodiment, a firstdirectional control valve 4-1 and a second directional control valve 4-2are connected to the discharge passage 2 of the hydraulic pump 1 throughthe pressure compensation valve unit 3 according to the presentinvention of the structure shown in FIG. 3, and furthermore, a thirddirectional control valve 4-3, a forth directional control valve 4-4 anda fifth directional control valve 4-5 are connected to the dischargepassage 2 of the hydraulic pump 1 respectively through the conventionalfirst, second and third pressure compensation valve units 3-1, 3-2 and3-3 shown in FIG. 1.

A first actuator 5-1 is a blade cylinder of a hydraulic power shovel, asecond actuator 5-2 is a boom swing cylinder, a third actuator 5-3 is anarm cylinder, a fourth actuator 5-4 is a bucket cylinder and a fifthactuator 5-5 is a boom cylinder. A blade cylinder as the first actuator5-1 is less used in frequency based on working nature of the powershovel.

According to the above structure, the outlet side of the pressurereducing valve 7 of the pressure compensation valve unit 3 of thepresent invention is connected to all of the outlet sides of thepressure reducing valves 7 of the first, second and third pressurecompensation valve units 3-1, 3-2 and 3-3 and also connected to the loadpressure detection circuit 11, so that when all of the actuators 5-1 to5-5 are operated simultaneously, the highest load pressure is detectedby the load pressure detection circuit 11 and the highest load pressureis introduced to the pressure receiving portions d of the pressurereducing valves 7 of the respective pressure compensation valve units.

As mentioned above, when one of the actuators 5-1 and 5-2 and at leastone of the actuators 5-1 to 5-3 are operated simultaneously, thedischarge pressure oil from the hydraulic pump 1 can be distributed tothe respective actuators as like as in the case of location of fivepressure compensation valve units.

FIG. 9 represents the third embodiment of the pressure oil supply systemaccording to the present invention. In this embodiment, three actuators5 are connected respectively to the output side of the pressurecompensation valve unit 3 through three directional control valves 4.

In this arrangement, because of the reason that it is necessary to pushthe pressure reducing valve 7 of the pressure compensation valve unit 3in the communication direction thereof by the highest load pressuresamong the load pressures of the three actuators, the pressure selectivereceiving means 30 is composed of a first slider 90 and a second slider91 which are operatively connected to each other, wherein a firstpressure receiving portion 92 pushing the first slider 90 toward thesecond slider 91 is connected to the load pressure detection port 4b ofone of the directional control valves 4 through the load pressureintroducing passage 8, a second pressure receiving portion 93 of thefirst slider 90 and a first pressure receiving portion 94 of the secondslider 91 are connected to another load pressure detection port 4b ofanother directional control valve 4 through another load pressureintroducing passage 8, and a second pressure receiving portion 95 of thesecond slider 91 and the pressure receiving portion c of the pressurereducing valve 7 are connected to still another load pressure detectionport 4b of the remaining directional control valve 4 through stillanother load pressure introducing passage 8.

According to the arrangement described above, when the load pressureacting on the first pressure receiving portion 92 is the highest one,the first slider 90 pushes the pressure reducing valve 7 toward thecommunication direction thereof through the second slider 91, when theload pressure acting on the second pressure receiving portion 93 and thefirst pressure receiving portion 94 is the highest one, the secondslider 91 pushes the pressure reducing valve 7 in the communicationdirection thereof after the first slider 90 is pushed leftwardly to itsstroke end portion, and when the load pressure acting on the secondpressure receiving portion 95 and the pressure receiving portion c isthe highest one, the pressure reducing valve 7 is pushed toward thecommunication direction thereof after the first and second sliders 90and 91 are pushed to the stroke end portions.

As mentioned above, it is allowed to locate only one pressurecompensation valve unit 3 for three actuators 5, and at a time when twoor three actuators 5 are simultaneously operated, the pressurecompensation of the supply pressure oil can be done by the highest loadpressure.

FIG. 10 shows a concrete structure of the pressure compensation valveunit 3 used for the third embodiment described above. As like thestructure shown in FIG. 4, the pressure compensation valve unit 3 isprovided for the valve block 40 of the directional control valve 4, andtwo free pistons 67 are fitted, in the axial direction thereof, to thesmall diameter rod 65 of the spool 66 constituting the pressure reducingvalve 7 to form a fourth pressure receiving chamber 95 between theadjacent free pistons 67. This fourth pressure receiving chamber 95corresponds to the second pressure receiving portion 93 and the firstpressure receiving portion 94 shown in FIG. 9 and is opened to the matedface of the valve block 40 through a fifth communication hole 96.

Furthermore, as shown in FIG. 11, the remaining two directional controlvalves 4 of the three ones shown in FIG. 9 has substantially the samestructure as that of the directional control valve 4 described withreference to FIG. 5, and the valve block 40 of one of these directionalcontrol valves 4 is connected to one of the mated faces of the valveblock 40 of the directional control valve 4 provided with the pressurecompensation valve unit 3, the valve block 40 of the other directionalcontrol valve 4 is connected to the other mated face of the valve block40 of the directional control valve 4 provided with the pressurecompensation valve unit 3, the second communication hole 75 of the valveblock 40 of the directional control valve 4 provided with the pressurecompensation valve unit 3 is communicated with the third communicationholes 76 of the valve blocks 40 of two directional control valves 4,respectively, the first communication hole 74 is communicated with thefourth communication hole 77 of the valve block 40 of one of the abovedirectional control valves 4, and the third communication hole 99 iscommunicated with the fourth communication hole 77 of the valve block 40of the other directional control valve 4.

According to such arrangement, the output pressure (pressure oilcompensated in pressure) of the pressure compensation valve unit 3 issupplied to the pump ports 46 of the directional control valves 4 bycoupling, in a mated state, the respective valve blocks 40, and thepressure (load pressure) of the second load pressure detection port 48of one of the directional control valves 4 is supplied to the firstpressure receiving chamber 68 and the pressure (load pressure) of thesecond load pressure detection port 48 of the other one of thedirectional control valve 4 is supplied to the third pressure receivingchamber 95. Accordingly, the arrangement of FIG. 11 attainssubstantially the same function as that of the pressure compensationvalve unit 3 shown in FIG. 9.

FIG. 12 represents the fourth embodiment of the pressure oil supplysystem according to the present invention. In this embodiment, thepressure selective receiving means 30 is provided with a high pressurepriority valve 100 having two inlets which are connected to the loadpressure introducing passages 8, respectively, and an outlet which isconnected to the pressure receiving portion c of the pressure reducingvalve 7 through a circuit line 101. According to this arrangement, thehighest load pressure is applied to the pressure receiving portion c ofthe pressure reducing valve 7 to thereby push the same in thecommunication direction.

FIG. 13 represents the fifth embodiment of the pressure oil supplysystem according to the present invention. In this embodiment, thepressure selective receiving means 30 is equipped with first and secondhigh pressure priority valves 102 and 103, in which the first highpressure priority valve 102 has two inlets which are connected to oneload pressure introducing passage 8, respectively, a circuit line 104connected to an outlet thereof and the remaining load pressureintroducing passage 8 are connected to two inlets of the second highpressure priority valve 102, and a circuit 105 connected to an outletthereof is connected to the pressure receiving portion c of the pressurereducing valve 7. According to this arrangement, the highest one of theload pressures in the three load pressure introducing passages 8 isapplied to the pressure receiving portion c of the pressure reducingvalve 7 to thereby push the same in the communication direction.

As mentioned hereinabove, according to the present invention, since thepressure reducing valve 7 of the pressure compensation valve unit 3 ispushed in the direction communicating the inlet and outlet sides by thehighest load pressure in the plurality of load pressures, the pressurecompensation of the supply pressure oil can be performed by the highestload pressure in the plurality of load pressures.

Accordingly, since the pressure oil can be supplied to the plurality ofactuators regardless of the magnitude of the load pressure even in thearrangement in which the pressure oil is supplied to the plurality ofthe actuators through one pressure compensation valve unit 3, the numberof the pressure compensation valve unit 3 to be used can be reduced incomparison with the number of the actuators arranged, thus reducing themanufacturing cost.

Although the present invention has been illustrated and described withrespect to exemplary embodiments thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,deletions and additions may be made thereto without departing from thescopes of the present invention. Therefore, the present invention shouldnot be understood as limited to the specific embodiments described abovebut to include all possible embodiments which can be embody within ascope encompassed and equivalents thereof with respect to the featuresrecited in the appended claims.

We claim:
 1. A pressure compensation valve unit comprising:a check valvewhich is pushed in an opening direction thereof by an inlet sidepressure and in a closing direction thereof by an outlet side pressure;and means, including a pressure reducing valve, actuating to establishcommunication between the inlet side and the outlet side of the checkvalve and block the communication therebetween, said pressure reducingvalve means being pushed in the blocking direction by a pressure in apressure receiving chamber to push the check valve in the closingdirection thereof, and being pushed in the communication direction witha highest pressure selected in a plurality of pressures by a pressureselective receiving means, and communicating said outlet side with saidpressure receiving chamber.
 2. A pressure compensation valve unitaccording to claim 1, wherein said pressure selective receiving means isprovided with a slider for pushing said pressure reducing valve in thecommunication direction thereof and a pressure receiving portion adaptedto receive a pressure for pushing the pressure reducing valve in thecommunication direction and wherein when a pressure acting on saidslider is higher than a pressure acting on said pressure receivingportion, said pressure reducing valve is pushed by said slider in thecommunication direction thereof.
 3. A pressure compensation valve unitaccording to claim 1, wherein said pressure selective receiving meanscomprises a pressure receiving portion receiving a pressure for pushingsaid pressure reducing valve in the communication direction and a highpressure priority valve for supplying a pressure oil on the highestpressure side in a plurality of pressure oils to said pressure receivingportion.
 4. A pressure compensation valve unit comprising:a check valveprovided with a check valve bore to which an inlet port and an outletport are opened and a spool inserted into said check valve bore, adaptedto communicate said inlet port with said outlet port and to block thecommunication therebetween, pushed in the communication direction by apressure at said inlet port and pushed in the blocking up direction by apressure at said outlet port; and a pressure reducing valve providedwith a pressure reducing valve bore to which a first port and a secondport are opened, a spool inserted into said pressure reducing valveport, adapted to communicate said first port with said second port andto block the communication therebetween and having a small diameter rodopposing to said check valve, a third pressure receiving chamberreceiving a pressure for pushing said spool in the blocking up directionthrough the communication with said second port, and first and secondpressure receiving chambers formed on both end sides of a free pistonslidably fitted to said small diameter rod and adapted to receive apressure for pushing said spool in the communication direction thereof,wherein load pressures of different actuators are introduced into saidfirst and second pressure receiving chambers.
 5. A pressure compensationvalve unit according to claim 4, wherein a plurality of free pistons arefitted to the small diameter rod of the spool of said pressure reducingvalve, a further pressure receiving chamber for receiving a pressure forpushing said spool in the communication direction is formed betweenadjacent free pistons of said plurality of free pistons, and loadpressures of other actuators are introduced into said other pressurereceiving chambers.
 6. A pressure oil supply system wherein a pressurecompensation valve unit is disposed in a discharge passage of ahydraulic pump, said pressure compensation valve unit comprising:a checkvalve which is pushed in an opening direction thereof by an inlet sidepressure and in a closing direction thereof by an outlet side pressureand a pressure reducing valve cooperating with said check valve andactuating to establish communication between the inlet side and theoutlet side of said check valve and block the communicationtherebetween, said pressure reducing valve having a pressure reducingvalve member pushed in the blocking direction by a pressure in apressure receiving chamber to push the check valve in the closingdirection thereof, said pressure reducing valve member being pushed inthe communication direction with a highest pressure in a plurality ofpressures selected by a selection pressure receiving means, andcommunicating said outlet side with said pressure chamber; a pluralityof actuators connected to the output side of said pressure compensationvalve unit through a plurality of directional control valves; thedischarge passage of said hydraulic pump connected to the inlet side ofthe pressure reducing valve of said pressure compensation valve unit;and load pressure of the respective actuators are introduced into saidpressure selective receiving means so as to push said pressure reducingvalve by the highest load pressure.
 7. A pressure oil supply systemaccording to claim 6, wherein said pressure selective receiving means isprovided with a slider for pushing said pressure reducing valve in thecommunication direction and a pressure receiving portion receiving apressure for pushing said pressure reducing valve in the communicationdirection and wherein when a pressure acting on said slider is higherthan a pressure acting on said pressure receiving portion, said pressurereducing valve is pushed in the communication direction by said slider.8. A pressure oil supply system according to claim 6, wherein saidpressure selective receiving means comprises a pressure receivingportion receiving a pressure for pushing said pressure reducing valvemember in the communication direction and a high pressure priority valvefor supplying a pressure oil on the highest pressure side in a pluralityof pressure oils to said pressure receiving portion.
 9. A pressure oilsupply system provided with a pressure compensation valve unitcomprising:a check valve provided with a check valve bore to which aninlet port and an outlet port are opened and a spool inserted into saidcheck valve bore, adapted to communicate said inlet port with saidoutlet port and to block the communication therebetween, pushed in thecommunication direction by a pressure at said inlet port and pushed inthe blocking up direction by a pressure at said outlet port; and apressure reducing valve provided with a pressure reducing valve bore towhich a first port and a second port are opened, a spool inserted intosaid pressure reducing valve port, adapted to communicate said firstport with said second port and to block the communication therebetweenand having a small diameter rod opposing to said check valve, a thirdpressure receiving chamber receiving a pressure for pushing said spoolin the blocking up direction through the communication with said secondport, and first and second pressure receiving chambers formed on bothend sides of a free piston slidably fitted to said small diameter rodand adapted to receive a pressure for pushing said spool in thecommunication direction thereof; and wherein a plurality of actuatorsare connected to the output side of said pressure compensation valveunit through a plurality of directional control valves; the dischargepassage of said hydraulic pump is connected to the inlet side of thepressure reducing valve of said pressure compensation valve unit; andload pressures of different actuators are introduced into the first andsecond pressure receiving chambers of said pressure reducing valve tothereby push said pressure reducing valve in the communication directionwith the highest load pressure.
 10. A pressure oil supply systemaccording to claim 9, wherein a plurality of free pistons are fitted tothe small diameter rod of the spool of said pressure reducing valve, afurther pressure receiving chamber for receiving a pressure for pushingsaid spool in the communication direction is formed between adjacentfree pistons of said plurality of pistons, and load pressures of otheractuators to said other pressure receiving chambers are introduced. 11.A pressure oil supply system according to any one of claims 6 to 10,wherein a load pressure detection line is connected to the outlet sideof said pressure reducing valve.
 12. A pressure compensation valve unit,comprising:a check valve which is pushed in an opening direction thereofby an inlet side pressure and in a closing direction thereof by anoutlet side pressure; and a pressure reducing valve, cooperating withsaid check valve, actuating to establish communication between the inletside and the outlet side of the check valve and block communicationtherebetween, said pressure reducing valve provided with a pressurereducing valve bore to which a first port and a second port are opened,a spool inserted into said pressure reducing valve port, adapted tocommunicate said first port with said second port and to block thecommunication therebetween and having a small diameter rod opposing tosaid check valve, a third pressure receiving chamber receiving apressure for pushing said spool in the blocking direction through thecommunication with said second port, and first and second pressurereceiving chambers formed on both end sides of a free piston slidablyfitted to said small diameter rod and adapted to receive a pressure forpushing said spool in the communication direction thereof; and apressure selective receiving means for selectively receiving a highestpressure in a plurality of pressures in said first and second pressurereceiving chambers to push said spool in the communication thereof. 13.A pressure compensation valve unit according to claim 12, wherein saidpressure selective receiving means is provided with a slider for pushingsaid pressure reducing valve in the communication direction thereof anda pressure receiving portion adapted to receive a pressure for pushingthe pressure reducing valve in the communication direction and whereinwhen a pressure acting on said slider is higher than a pressure actingon said pressure receiving portion, said pressure reducing valve ispushed by said slider in the communication direction thereof.
 14. Apressure compensation valve unit according to claim 12, wherein saidpressure selective receiving means comprises a pressure receivingportion receiving a pressure for pushing said pressure reducing valve inthe communication direction and a high pressure priority valve forsupplying a pressure oil on the highest pressure side in a plurality ofpressure oils to said pressure receiving portion.